Toward a mesoscale marine hydrological and meteorological observation network in the South China Sea

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Toward a mesoscale marine hydrological and meteorological observation network in the South China Sea Lei Yang 1, Jian Huang 2, Xin Wang 1, Lili Zeng 1, Rui

1, Dongxiao Wang 1 * 1 State Key Laboratory of Tropical Oceanography, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou, China

1 Toward a mesoscale marine hydrological and meteorological observation network in the South China Sea Lei Yang 1, Jian Huang 2, Xin Wang 1, Lili Zeng 1, Rui Shi 1, Yunkai He 1, Qiang Xie 3, Shengan Wang 1, Rongyu Chen 1, Jinnan Yuan 2, Qiang Wang 1, Ju Chen 1, Tingting Zu 1, Jian Li 1, Dandan Sui 1, Shiqiu Peng 1, Dongxiao Wang 1 * 1 State Key Laboratory of Tropical Oceanography, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou, China 2 Guanghou Institute of Tropical and Marine Meteorology, China Meteorology Administration, Guangzhou, China Bulletin of American Meteorological Society, 2015

2 Regional observations in other basins The Bay of Bengal Monsoon Experiment The Arabian Sea Monsoon Experiment The Joint Air Sea Monsoon Experiment The Surface Ocean Lower Atmosphere Study The Coupled Boundary Layers and Air-Sea Transfer program. Large scale air-sea observations The 8-year ( ) World Ocean Circulation The Global Ocean Observing System (GOOS) The Tropical Atmosphere Ocean/Triangle trans-ocean Buoy Network (TAO/TRITON).

5 3 12 8 8 8 2 6 10 9 3 5 1 5 11 5 2 3 3 13 8 7 10 8 17 11 13 8 3 3 11 3 5 4 12 2 5 6 5 9 3 4 5 6 13 6 3 4 6 1 13 4 11 1 5 7 6 3 4 3 3 1 2 3 5 5 1 2 9 11 2 3 6 5 2 2 1 4

3 Scientific background Upwelling Shu et al., 2011 Eddy o N Vietnam CHINA Taiwan Luzon Strait Luzon Chen et al., o E Intraseasonal cold filament Xie et al., 2007 SST double peak Interannual variability of SST is mostly related to ENSO. SST double peak Wang et al., 2006 The air-sea interaction in the SCS is strongly related with Asian monsoon

Intraseasonal variability of latent-heat flux in the SCS Intraseasonal latent heat flux has two spectral peaks around 28 35 and 49 56 days Standard deviation of 30-60d latent heat flux The

4 Intraseasonal variability of latent-heat flux in the SCS Intraseasonal latent heat flux has two spectral peaks around and days Standard deviation of 30-60d latent heat flux The intra-seasonal latent-heat flux variations in summer are remarkably different from those in winter. Intraseasonal latent-heat flux fluctuations are closely related to monsoon. Correlated to southwesterly winds in summer, and primarily associated with northesterly winds and Q a in winter. Zeng, Wang et al. (2009) TAC

Intraseasonal variability of cold filament off Vietnam coast in the SCS The intraseasonal cold filaments tend to reduce the local wind speed and precipitation due to increased static stability in the

5 Intraseasonal variability of cold filament off Vietnam coast in the SCS The intraseasonal cold filaments tend to reduce the local wind speed and precipitation due to increased static stability in the near-surface atmosphere, indicating the existence of an ocean atmosphere feedback Intraseasonal variations of strong upwelling along the south coast of Vietnam, and a cold filament that stretches eastward at about 12N from the coast during June September each in response to the intraseasonal variations of Asian summer monsoon. Xie et al. (2007) JGR-Oceans; Wang et al. (2002), CSB

6 Convective and stratiform rainfall and heating associated with the summer monsoon over the South China Sea (TRMM-based observation) El Nino years Jan Feb Mar Apr May onset Retreat Only increase since May Latent heating Convective rainfall Stratiform rainfall Ratio of convective to stratiform rainfall Latent heating Increase rapidly Latent heating and the ration of convective to stratiform rainfall can characterize the seasonal march of the SCS summer monsoon Li, Wang et al. (2009) TAC La Nina years

Impact of tropical cyclone development on the instability of South Asian High and the summer monsoon onset over Bay of

generate zonal asymmetric PV forcing, with positive vorticity advection to its east and negative advection to its west.

a slowly westward propagating Rossby wave accompanied by a westward shift of the high Potential vorticity advection.

7 Impact of tropical cyclone development on the instability of South Asian High and the summer monsoon onset over Bay of Bengal Nargis Neoguri 12460gpm Strong latent heating related with Neoguri can enhance the development of the SAH aloft and generate zonal asymmetric PV forcing, with positive vorticity advection to its east and negative advection to its west. High PV Following the decay of Neoguri, this asymmetric forcing leads to instability development of the SAH, presenting as a slowly westward propagating Rossby wave accompanied by a westward shift of the high Potential vorticity advection. Wu, Wang et al. (2013) Clim Dyn. Divergence A strong upper tropospheric divergence on the southwest of the SAH also shifts westward

8 As the main moisture source of the SCS summer monsoon, as well as being a region with high frequency of mesoscale eddies and severe weather systems, e.g. tropical cyclones, storm surges. The SCS imposes a profound impact on the weather and climate change of the surrounding landmass. Thus, there are significant potential benefits to an improved understanding of the regional circulation and air sea interactions taking place in the SCS. However, progress is hindered by a lack of three dimensional mesoscale observations of the key dynamic processes in both atmosphere and ocean over the SCS.

Little mapping During 1978-1984, observation mainly focus on the costal shelf for the studies of Pearl River plume Earlier Observations 1978-1984 (Ou et al.

9 Little mapping During , observation mainly focus on the costal shelf for the studies of Pearl River plume Earlier Observations (Ou et al. 2009) 1960s/1980s There are some deep cast data in the northern South China Sea during 1960s and early 1980s, most of which reached 2000m depth or deeper (Liu et al. 2012)

1989-1999 During 1989-1999, several cruises

10 Earlier Observations Most of these earlier observations only have CTD measurements During , several cruises were made in the southern South China Sea (Fang et al. 2012)

11 Earlier Observations IOP: The SCS Monsoon Experiment (SCSMEX), conducted between 1996 and 2001 with a field phase from 1 May to 3 August 1998, was a major international field experiment set up to study the physical processes involved in the onset, maintenance, and variability of the SCS summer monsoon

12 The SCS observational network is designed to Provide simultaneous atmospheric and oceanic observations, which is essential for air sea coupling studies, particularly on the synoptic timescale. Provide vertical profiles of oceanic and atmospheric variables, which can then be used to study the baroclinic structures of the atmospheric and oceanic circulation in the SCS. Provide data that can be used to evaluate satellite observations and to assess/calibrate model outputs.

In 2004, the SCS Institute of Oceanology (SCSIO) conducted a cruise in the northern SCS (18 23N, 110 120E) during late

13 In 2004, the SCS Institute of Oceanology (SCSIO) conducted a cruise in the northern SCS (18 23N, E) during late summer (August September) 8 transects were carefully designed based on research interests and important scientific issues.

14 Since 2006, the SCSIO open cruise has carried a radiometer and conducted GPS sounding. GPS sounding balloons are launched regularly during each cruise to obtain vertical profiles of wind, air temperature and humidity. GPS sounding AWS (including longwave and showave radiometer)

15 Fixed multi-function observation platforms in the ocean complement cruise observations by providing long-term and continuous realtime data. ADCP, surface buoy, AWS at Xisha station

The 20 m Xisha Island air sea boundary flux tower located 97 m offshore of Yongxing Island (16.84N, 112.

16 The 20 m Xisha Island air sea boundary flux tower located 97 m offshore of Yongxing Island (16.84N, E), has been in operation since The tower is equipped for gradient and eddy covariance observations for the measurement of air sea boundary fluxes

17 The observational data from the network can be used for both research and real-time environmental monitoring. To date, the observation datasets along the western boundary have formed a clear monitoring network for the coastal area of southern China

18 The Marine Meteorological Science Experiment Base at Bohe was jointly established in 2006 by Guangzhou Institute of Tropical and Marine Meteorology and Maoming Meteorological Bureau under the Guangdong Meteorological Service of the China Meteorological Administration

20 7 buoys, 3 stations 3 platforms, 30 cruises including 10 SCSIO open cruises in the northern SCS, 4 Xisha cruises, 5 southern SCS cruises, four NSFC open cruises, and 7 other cruises

22 Observations have been used in several scientific issues Regional circulation in the SCS since the 1990s The formation of SCS warm current Upwelling Freshening of 2012 Eddy activities Processes in the MABL SST perturbations associated with eddies, oceanic fronts Air sea boundary fluxes related to monsoon onset and retreat, sea fog Atmospheric ducts Atmospheric disturbance and tropical cyclones Synoptic perturbations and their interannual variability Air-sea interactions during tropical cyclone passages

Scientific applications The deflection of the SCS warm current ADCP The eastern part of the SCS Warm Current flows eastward along the isobath, and then veers off toward the deep sea while it flows

23 Scientific applications The deflection of the SCS warm current ADCP The eastern part of the SCS Warm Current flows eastward along the isobath, and then veers off toward the deep sea while it flows around the Dongsha. ADCP and CTD confirmed the deflection. Combining the observations and model simulation, it is found that JEBAR plays an important role in the deflection ADCP Wang et al. (2013) JGR

Scientific applications Upwelling in the northern SCS

cold near-bottom water climbed up the slope and the

NSCS. Assimilating CTD measurements obtained from SCOPE

et al. (2011a) CSR; Shu et al. (2011b OM); Wang et al.

5 times) large-scale current Topographically induced

24 Scientific applications Upwelling in the northern SCS SCOPE-PP CTD Model Without upwelling favorable wind, the cold near-bottom water climbed up the slope and the subsurface upwelling took place between 20 and 100 m in the NSCS. Assimilating CTD measurements obtained from SCOPE (2008) into a regional ocean model Downwelling favorable Shu et al. (2011a) CSR; Shu et al. (2011b OM); Wang et al., (2014) JGR Exp.3 (Exp. 4) half (1.5 times) large-scale current Topographically induced upwelling is sensitive to alongshore largescale currents, which have an important contribution to the upwelling intensity

25 Scientific applications Freshening of 2012 in the northern SCS Aquarius SSS (v3.0) In situ observations 2012 A freshening of up to 0.4 psu in the upper ocean of the northern SCS in 2012 using satellite observations, which were evaluated against in situ observations from the SCS The study suggested that the freshening in 2012 might have been caused by the combined effect of abundant local freshwater flux and limited Kuroshio intrusion. Zeng et al. (2013) JGR

Scientific application SST perturbations associated with eddies, oceanic fronts Drifting buoys

May Vertical geostrophic currents The CTD and ADCP data, as well as those from drifting buoys,

26 Scientific application SST perturbations associated with eddies, oceanic fronts Drifting buoys Temperature Feb. CTD Mar. Apr. May Vertical geostrophic currents The CTD and ADCP data, as well as those from drifting buoys, successfully captured the vertical structure of the three eddies and their evolutions Nan et al. (2011) JGR; He et al. (2013) AOS Salinity The formation of the SMH is attributed to both wind forcing and the release of potential energy by the winter monsoon Observations confirms the existence of a recurring spring mesoscale eddy with a warm core and low salinity (with interannual variation on location and size)

Scientific applications SST perturbations associated with eddies, oceanic fronts In 2010, an extremely large and longlasting warm eddy was observed in the SCS to be moving

The CTD and XBT obtained during the 2010 warm-eddy cruise were used to explore the eddy s vertical structure A strong El Niño event in 2009/2010 altered the intensity and direction

27 Scientific applications SST perturbations associated with eddies, oceanic fronts In 2010, an extremely large and longlasting warm eddy was observed in the SCS to be moving northward from the south of the Xisha Islands. The CTD and XBT obtained during the 2010 warm-eddy cruise were used to explore the eddy s vertical structure A strong El Niño event in 2009/2010 altered the intensity and direction of the summer monsoon, resulting in the disappearance of this pattern and the northward movement of a preexisting warm eddy along the Vietnam coast. During this northward movement, the western boundary current cascaded energy to the eddy, which led to its continuing growth in both strength and size. Chu et al. (20114) JGR;

Scientific applications Processes in the MABL Data from the Xisha flux tower September Both boundary momentum and heat flux exchanges responded strongly to the retreat of monsoon near around 7

28 Scientific applications Processes in the MABL Data from the Xisha flux tower September Both boundary momentum and heat flux exchanges responded strongly to the retreat of monsoon near around 7 September 2013 Satellite-derived air specific humidity is verified against 1016 high-resolution radiosonde profiles from 1998 to 2012 and the time series from the 26 AWS at Xisha during SCSSLH shows the highest spatial resolution and realistic values in the SCS, with an exception along the northern continental shelf. The other five products overestimate the latent heat flux systematically. Improved estimates of bulk variables based on in situ measurements has contributed the better representation of daily SCSSLH, which further highlights the unique role of high-quality meteorological measurements and atmospheric weather stations in evaluating the air sea interaction in the SCS. Shi et al. (2014), AHEMS; Wang et al. (2014), JAOT

km away the Xisha Station Using the AWS and buoy data from Xisha Stations, studies have shown that

29 Scientific applications Air-sea interactions during tropical cyclone passages A total of 52 tropical cyclones passed over the SCS during the period , and 21 of those 52 were found to be less than 400 km away the Xisha Station Using the AWS and buoy data from Xisha Stations, studies have shown that atmospheric variables and air sea interaction during tropical cyclone passages experience significant changes Wang et al., 2012

30 The mesoscale observation network in the SCS consists of both oceanic and meteorological observations during cruises and at stations. The network was designed based on the characteristics of the regional circulation and air sea interaction over the SCS. The observations were mainly concentrated in the dynamically active areas. The oceanic processes in these key regions represent the main dynamic characteristics of the SCS, and their related air sea interactions have direct impacts upon the economies and human activities of the surrounding countries. Collecting observations at mesoscale resolution in these key regions (in terms of both horizontal mapping and vertical profiles) is an important approach to investigating regional air sea coupling in the SCS under current research-funding conditions.

31 From SCSMEX to YMC

32 Workgroup of Chinese YMC Guangzhou, 17 Nov., 2015

33 Participators Dongixao Wang and Xin Wang: South China Sea Institute of Oceanology, Chinese Academy of Sciences Chongyin Li and Jian Ling: Institute of Atmospheric Physics, Chinese Academy of Sciences Song Yang: Sun Yat-Sen University Weidong Yu and Lin Liu: First Institute of Oceanography, State Oceanic Administration Qilin Wang: Guangzhou Institute of Tropical and Marine Meteorology, China Meteorological Administration Peiqun Zhang: National Climate Center, China Meteorological Administration

34 Planed Observation Maintain ground-base or island-base air-sea flux tower in Sri Lanka, Xisha Island, Bohe Build a air-sea flux tower with other institutes or universities in MC Conduct RV Investigator and buoy deployed in southern South China Sea Apply grant fund from NSFC and other way

35 Research Interests Circulations associated with ITF and SCSTF Air-sea interaction in the South China Sea and its climate impacts Upper ocean processes associated with ITF and mixing MC and MJO MC convection; impacts of MC on MJO; impacts of MC and MJO on regional climate (i.e., equator currents, Austrlia monsoon, South China Sea summer monsoon ) Regional model development

36 Thank you for your attention! URL:

Circulation in the South China Sea in summer of 1998

Circulation in the South China Sea in summer of 1998 LIU Yonggang, YUAN Yaochu, SU Jilan & JIANG Jingzhong Second Institute of Oceanography, State Oceanic Administration (SOA), Hangzhou 310012, China;